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The effects of inorganic ions on the catalytic activity of pig liver phosphofructokinase were investigated. High concentrations of monovalent anions inhibit the enzyme by decreasing max with little change in the Hill coefficient. The efficiency of inhibition follows the

series NO3- < Cl- < ClO3- = Br- < I- < SCN-, which is similar to the classical Hofmeister series. Low concentrations (<2 mM) of the divalent anions Pi, sO4 2-, s2O3 2- SO32- , and MoO42- all activate the enzyme by changing the kinetics from sigmoidal to hyperbolic, with no change in V max . However, B4o72- has no effect. The apparent dissociation constants of the activating anions for the enzyme were calculated from activation curves for the anions at 0.5mM ATP and 1.0m MF6p.The activation curve for so4-2 is sigmoidal; the activation curves for the other activating anions are hyperbolic. The monovalent cations K+, NH4+ , and Rb+ activate the enzyme by increasing V max without greatly affecting the Hill coefficient.

However, the [S}0.5 for F6P is decreased by these cations to an extent directly proportional to their ionic volumes.

The monovalent cations Li + , Na+ , and C s + have no activating effect; instead, high concentrations of these cations inhibit the enzyme in a manner similar to the monovalent anions. The efficiency of inhibition follows the series Cs+ < Na+ < Li+ .

Possible mechanisms of inhibition and activation by the various inorganic ions and the physiological signifi­cance of the activating anions and cations are discussed.



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UNM Biology Department

First Committee Member (Chair)

John Trujillo

Second Committee Member

Oswald G. Baca

Third Committee Member

David L. Vander Jagt

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